1. Field of Invention
The present invention relates to a solid-state imaging device of a threshold voltage modulation system.
2. Description of Related Art
In recent years, mobile electronic equipment, such as cellular phones and digital cameras, have been equipped with a small solid-state imaging device. As such a solid-state imaging device, a MOS solid-state imaging device of a threshold voltage modulation system has been developed.
The MOS solid-state imaging device of a threshold voltage modulation system can include a plurality of pixels arranged in a matrix. Each of the pixels includes a single of photo diode and a single of transistor. An accumulation region referred to as a hole pocket, where holes tend to be collected, is formed below a gate electrode of the transistor. The photo diode generates holes depending on the intensity of incident light. The generated holes are accumulated in the accumulation region. The threshold voltage of the transistor changes depending on the number of holes accumulated in the accumulation region. Then, source voltage depending on the intensity of incident light, namely pixel data is obtained by reading out the source voltage that changes in response to the change of the threshold voltage. Using a plurality of pixel data corresponding to the plurality of pixels allows one image data to be produced. Details about the MOS solid-state imaging device of a threshold voltage modulation system are disclosed in, for example, Japanese Unexamined Patent Application Publication No. 11-195778 and the like.